Alkaline cell with improved cathode

FIELD OF THE INVENTION

This invention relates to an aqueous alkaline cell with a cathode mixture comprising silver copper oxide AgCuO

2

or Ag

2

Cu

2

O

3

or mixtures thereof.

BACKGROUND OF THE INVENTION

Conventional alkaline electrochemical cells have an anode comprising zinc and a cathode comprising manganese dioxide. The cell is typically formed of a cylindrical casing. The casing is initially formed with an enlarged open end and opposing closed end. After the cell contents are supplied, an end cap with insulating plug is inserted into the open end. The cell is closed by crimping the casing edge over an edge of the insulating plug and radially compressing the casing around the insulating plug to provide a tight seal. A portion of the cell casing at the closed end forms the positive terminal.

Primary alkaline electrochemical cells typically include a zinc anode active material, an alkaline electrolyte, a manganese dioxide cathode active material, and an electrolyte permeable separator film, typically of cellulose or cellulosic and polyvinylalcohol fibers. The anode active material can include for example, zinc particles admixed with conventional gelling agents, such as sodium carboxymethyl cellulose or the sodium salt of an acrylic acid copolymer, and an electrolyte. The gelling agent serves to suspend the zinc particles and to maintain them in contact with one another. Typically, a conductive metal nail inserted into the anode active material serves as the anode current collector, which is electrically connected to the negative terminal end cap. The electrolyte can be an aqueous solution of an alkali metal hydroxide for example, potassium hydroxide, sodium hydroxide or lithium hydroxide. The cathode typically includes particulate manganese dioxide as the electrochemically active material admixed with an electrically conductive additive, typically graphite material, to enhance electrical conductivity. Optionally, polymeric binders, and other additives, such as titanium-containing compounds can be added to the cathode.

The manganese dioxide used in the cathode is preferably electrolytic manganese dioxide (EMD) which is made by direct electrolysis of a bath of manganese sulfate and sulfuric acid. The EMD is desirable since it has a high density and high purity. The resistivity of EMD is fairly low. An electrically conductive material is added to the cathode mixture to improve the electric conductivity between individual manganese dioxide particles. Such electrically conductive additive also improves electric conductivity between the manganese dioxide particles and the cell housing, which also serves as cathode current collector. Suitable electrically conductive additives can include, for example, conductive carbon powders, such as carbon blacks, including acetylene blacks, flaky crystalline natural graphite, flaky crystalline synthetic graphite, including expanded or exfoliated graphite. The resistivity of graphites such as flaky natural or expanded graphites can typically be between about 3×10

−3

ohm-cm and 4×10

−3

ohm-cm.

It is desirable for a primary alkaline battery to have a high discharge capacity (i.e., long service life). Since commercial cell sizes have been fixed, it is known that the useful service life of a cell can be enhanced by packing greater amounts of the electrode active materials into the cell. However, such approach has practical limitations such as, for example, if the electrode active material is packed too densely in the cell, the rates of electrochemical reactions during cell discharge can be reduced, in turn reducing service life. Other deleterious effects such as cell polarization can occur as well. Polarization limits the mobility of ions within both the electrolyte and the electrodes, which in turn degrades cell performance and service life. Although the amount of active material included in the cathode typically can be increased by decreasing the amount of non-electrochemically active materials such as polymeric binder or conductive additive, a sufficient quantity of conductive additive must be maintained to ensure an adequate level of bulk conductivity in the cathode. Thus, the total active cathode material is effectively limited by the amount of conductive additive required to provide an adequate level of conductivity.

It is desirable that the cell have high service life under normal drain rates, for example, between about 50 milliAmp and 500 milliAmp and also perform well in higher power application, at current rates between about 0.5 and 2.0 Amp, for example, between about 0.5 Amp and 1.5 Amp. Such high power application corresponds to a power output between about 0.5 and 1.5 Watt or even higher up to about 2.0 Watt. In conventional zinc/MnO

2

cells the utilization of anode/cathode active materials falls off as the current drain or power output requirements move into the high power regime.

Although such alkaline cells are in widespread commercial use there is a need to improve the cell or develop a new type of cell that exhibits reliable performance and longer service life for normal applications such as flashlight, radio, audio recorders and portable CD players and desirably also performs even better than conventional zinc/MnO

2

cells in high power applications.

SUMMARY OF THE INVENTION

The invention is directed to a primary (nonrechargeable) electrochemical alkaline cell having an anode comprising zinc and a cathode mixture comprising silver copper oxide selected from the compounds AgCuO

2

or Ag

2

Cu

2

O

3

or any mixture of AgCUO

2

and Ag

2

Cu

2

O

3

. The term “silver copper oxide” as used herein, unless otherwise specified shall be understood to mean the compounds AgCuO

2

, Ag

2

Cu

2

O

3

or mixtures thereof. The anode and cathode include an aqueous alkaline solution, preferably aqueous KOH solution. Such cell of the invention can be conveniently referenced herein as a Zn/Silver copper oxide alkaline cell. The silver copper oxide is preferably in the form of a powder having an average particle size between about 1 and 100 micron. The cathode mixture includes a conductive material such as flaky crystalline natural graphite or flaky crystalline synthetic graphite including expanded graphite and graphitic carbon nanofibers. The term graphitic carbon nanofibers as used herein shall mean graphitic carbon fibers having a mean average diameter less than 1000 nanometers (less than 1000×10

−9

meter) (The term “average” or “mean average” as used herein shall mean the “arithmetic mean average” unless otherwise specified.) Preferably, the graphitic carbon nanofibers have a mean average diameter less than 500 nanometer, more preferably less than 300 nanometers. Desirably the graphitic carbon nanofibers have a mean average diameter between about 50 and 300 nanometers, typically between about 50 and 250 nanometers. The cathode mixture includes an aqueous KOH solution, desirably having a concentration of between about 30 and 40 percent by weight, preferably between 35 and 45 percent weight KOH in water.

It has been determined that in the Zn/Silver copper oxide alkaline cell of the invention the anode can comprise conventional gelled zinc anode compositions as in commercial use in conventional zinc/MnO

2

alkaline cells. By way of an example, not intended to be restrictive, the cathode can comprise the same composition as conventional cathode comprising MnO

2

as used in commercial zinc/MnO2 alkaline cells, except that the MnO

2

can be replaced in whole or in part by the AgCuO

2

or Ag

2

Cu

2

O

3

compounds, or any mixture of AgCuO

2

and Ag

2

Cu

2

O

3

compounds herein disclosed. The AgCuO

2

has been determined to have advantages when used as a cathode in alkaline cells. The copper in AgCuO

2

has a +3 valence and the silver a +1 valence. The Cu

+3

and Ag

+1

are available for reduction to copper metal and silver metal during discharge. As a result the AgCuO

2

has a high theoretical specific capacity, namely, 526 milliAmp-hour/g. This is much higher than the theoretical specific capacity of MnO

2

, which is 308 milliAmp-hour/g and higher than the theoretical specific capacity of AgO, which is 436 milliAmp-hour/g or Ag

2

O, which is 117 milliAmp-hour/g. Additionally, the presence of silver (Ag

+1

) and (Cu

+3

) in the AgCuO

2

compound causes an elevation in a Zn/AgCuO

2

alkaline cell's running voltage profile as compared to a Zn/MnO

2

or Zn/CuO alkaline cell. Ag

2

Cu

2

O

3

has copper at valence at +2 (Cu+2) which is lower than copper at valence +3 (Cu+3) in the AgCuO

2

compound, and therefore, has a theoretical specific capacity of 412 milliAmp-hour/g, which is lower than the specific capacity of 526 milliamp-hour/g for the AgCuO

2

.

The Zn/Silver copper oxide alkaline cell exhibits a higher running voltage profile and longer service life than Zn/MnO

2

cells in normal applications, e.g. at drains rates between about 50 and 600 milliamp. It also exhibits a high rate capability for high power applications, for example, at current drains between about 0.5 and 1.5 Amp or power applications between about 0.5 and 1.5 Watt. For example, at a drain rate of about 1 Amp, between about 75 and 80 percent of the theoretical capacity of the AgCuO

2

can be utilized in a Zn/AgCuO

2

alkaline cell. The AgCuO

2

, which has a copper valence of +3 (or Ag

2

Cu

2

O

3

) is nevertheless sufficiently stable in water or aqueous KOH electrolyte solution. With respect to AgCuO

2

, this compound does not react in water or aqueous KOH electrolyte during normal cell storage at room temperature as well as ambient temperatures between about −29° C. and 46° C. (−20° F. and 115° F.) to cause any significant degradation of the Cu+

3

valence.

In a preferred embodiment, the silver copper oxide (AgCuO

2

, or Ag

2

Cu

2

O

3

or mixtures thereof) comprises between about 82 and 90 percent by weight of the cathode mixture. In such embodiment the silver copper oxide can replace all of the manganese dioxide in the cathode. The performance of conventional Zn/MnO2 alkaline cells can also be improved if the silver copper oxide is used to replace a portion of the amount of MnO

2

conventionally used in the alkaline cell cathode. In such case the silver copper oxide can be mixed into the cathode with MnO

2

. In either case, whether the AgCuO

2

is used alone or in admixture with MnO

2

, the graphitic conductive material in the cathode, desirably comprises between about 2 and 10 percent by weight of the cathode, preferably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material desirably comprises expanded graphite or natural graphite alone or in any mixtures thereof. In such case the graphitic conductive material comprises between about 3 and 10 percent by weight of the cathode, desirably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material can contain only expanded graphite or only natural graphite or only graphitic carbon nanofibers, but can also contain natural graphite, expanded graphite and graphitic carbon nanofibers in any combination or mixture thereof. In such case the graphitic conductive material desirably comprises between about 4 and about 10 percent by weight of the cathode. The aqueous KOH solution desirably comprises between about 5 and 10 percent by weight of the cathode mixture. The aqueous KOH solution itself desirably comprises between about 30 and 40 percent by weight KOH, preferably between about 35 and 40 percent by weight KOH and about 2 percent by weight zinc oxide.

In one aspect the alkaline cell of the invention has an anode comprising-zinc and a cathode mixture comprising silver copper oxide in the form AgCuO

2

. Such cell, for example, an AA size cell, exhibits high capacity (mAmp-hrs) and high energy output (mWatt-hours) under discharge rates between about 500 and 1000 mAmp when compared to same size conventional alkaline cell having an anode comprising zinc and cathode comprising manganese dioxide. This advantage would also apply to other size cylindrical cells, for example, AAAA, AAA, C and D size cells as well as AA cells.

In another aspect the alkaline cell of the invention has an anode comprising zinc and a cathode mixture comprising silver copper oxide in the form of Ag

2

Cu

2

O

3

. Such cell, for example, an AA size cell, exhibits high capacity (mAmp-hrs) and high energy output (mWatt-hours) under discharge rates between about 500 and 1000 mAmp when compared to same size conventional alkaline cell having an anode comprising zinc and cathode comprising manganese dioxide. This advantage would also apply to other size cylindrical cells, for example, AAAA, AAA, C and D size cells as well as AA cells.

Although the embodiments herein are directed to a nonrechargeble cell, it may nevertheless be possible to produce a rechargeable cell with modified cathodes comprising AgCuO

2

designed to partially discharge to Ag

2

Cu

2

O

3

, which in turn could be recharged back to AgCuO

2

. Such cell, for example, could be an alkaline cell with a zinc anode discharging to zinc oxide, rechargeable back to zinc.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1

is a cross sectional cut-away view of an elongated cylindrical alkaline cell having the cathode of the invention.

FIG. 2

is a cross sectional view of a cylindrical button alkaline cell having the cathode of the invention.

DETAILED DESCRIPTION

A representative alkaline cell utilizing the cathode mixture of the invention is shown in FIG.

1

. The alkaline cell

810

comprises an elongated cylindrical casing

820

of steel, preferably nickel plated steel, having a closed end

814

and an open end

816

. The cell is preferably filled with cathode mixture

812

of the invention comprising silver copper oxide (AgCuO

2

, Ag

2

Cu

2

O

3

or mixtures thereof) which functions as cathode active material.

The copper in the compound AgCuO

2

has a +3 valence and the silver a +1 valence. The Cu

+3

and Ag

+1

is available for reduction to copper metal and silver metal during cell discharge. As a result the AgCuO

2

has a high theoretical specific capacity, namely, 526 milliAmp-hour/g. (This is calculated as follows: 1 electron has the charge of 1.602×10

−19

coulomb. Based on Avogadro's number there are 6.023×10

23

molecules per mole. 1 coulomb=1 Amp-sec. Assume theoretical reduction of the AgCuO

2

molecule during cell discharge on the basis of 4 electrons per molecule. Then, the theoretical capacity, milli-Amp per mol of AgCuO

2

, is 4 electrons/molecule×6.023×10

23

molecules/mol×1.602×10

−19

coulomb/electron=4×9.649×10

4

coulomb/mol or 4×9.649×10

4

Amp-sec/mol. The molecular weight of AgCuo

2

is 203.5. Thus, the theoretical capacity of AgCuO

2

is 4×9.649×10

4

Amp-sec/mol×1 hour/3600 sec×1 mol/203.5 g=0.526 Amp/g=526 milliAmp/g. The compound Ag

2

Cu

2

O

3

has a lower theoretical specific capacity of about 412 mAmp-hr/g.

The cathode mixture

812

contains a conductive material, preferably a graphitic conductive material such as flaky crystalline natural graphite or flaky crystalline synthetic graphite, preferably expanded graphites or graphitic carbon nanofiber and mixtures thereof.

The term “graphite” or “graphitic material” as used herein shall include natural and synthetic crystalline graphites, expanded graphites, graphitic carbons, and graphitic carbon fibers. A graphitic carbon has the characteristics of an ordered three-dimensional graphite crystalline structure consisting of layers of hexagonally arranged carbon atoms stacked parallel to each other as determined by X-ray diffraction. As defined in International Committee for Characterization and Terminology of Carbon (ICCTC, 1982), published in the

Journal Carbon

, Vol. 20, p. 445 a graphitic carbon embraces the varieties of substances consisting of elemental carbon in allotropic form of graphite irrespective of of structural defects. The term graphitic carbon as used herein shall be construed in this manner.

The term carbon fibers shall mean elongated strands of carbon having length to diameter ratio greater than 4, typically greater than 8. The length to diameter ratio of carbon fibers can be much higher, for example, greater than 100 or more. The term “natural crystalline graphite” as used herein shall mean graphite that is minimally processed, i.e., essentially in its geologically occurring natural crystalline form. The term “synthetic graphite” as used herein shall mean synthetically prepared or processed graphite. The term “synthetic graphite” as used herein unless further qualified is also intended to include expanded forms of graphite (including expanded graphite that has been exfoliated) and graphitic carbon nanofibers. The term “expanded graphite” is a recognized term of art, for example, the form of graphite generally as referenced in U.S. Pat. No. 5,482,798. Further, expanded graphite as used herein can be formed from natural and/or synthetic non-expanded graphite processed so as to have a uniaxially expanded crystal lattice. The extent of uniaxial expansion can be sufficiently large such that the expanded graphite particles can completely exfoliate (i.e., separate into thin laminae). The term “flaky” as commonly used in connection with graphites, (i.e., natural or synthetic flaky graphites) is intended to reflect that such graphites have a plate-like, non-expanded particle form.

The graphitic conductive material is added to the AgCuO

2

active material to form the cathode of the invention. The graphitic conductive material desirably comprises between about 2 and 10 percent by weight of the cathode mixture, preferably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material desirably comprises expanded graphite or natural graphite alone or in any mixtures thereof. In such case the graphitic conductive material comprises between about 3 and 10 percent by weight of the cathode, desirably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material can contain only expanded graphite or only natural graphite or only graphitic carbon nanofibers, but can also contain natural graphite, expanded graphite and graphitic carbon nanofibers in any combination or mixture thereof. In such case the graphitic conductive material desirably comprises between about 4 and about 10 percent by weight of the cathode. The aqueous KOH solution desirably comprises between about 5 and 10 percent by weight of the cathode mixture. It has been determined that expanded graphite provides a desirable graphitic conductive material when used alone or in admixture with natural graphite to be added to the AgCuO

2

cathode active material. However, the graphitic carbon nanofibers can also be added to form a portion of the graphitic conductive material as above mentioned. Such graphitic carbon nanofibers, per se, are referenced in the published art and specific methods of manufacture are disclosed, for example, in U.S. Pat. Nos. 5,594,060; 5,846,509 and 6,156,256.

The term graphitic carbon fibers as used herein shall mean carbon fibers having a graphitic carbon structure as defined by the International Committee for Characterization and Terminology of Carbon (ICCTC, 1982), published in the

Journal Carbon

, Vol. 20, p. 445. The graphitic carbon nanofibers as used herein shall mean graphitic carbon fibers having a mean average diameter less than 1000 nanometers (less than 1000×10

−9

meters). (The term “average” or “mean average” as used herein, unless otherwise specified, shall be understood to mean the arithmetic mean average.) Preferably, the graphitic carbon nanofibers have a mean average diameter less than 500 nanometer, more preferably less than 300 nanometers. Desirably the graphitic carbon nanofibers have a mean average diameter between about 50 and 300 nanometers, typically between about 50 and 250 nanometers. The graphitic carbon nanofiber useful in the cathode mixture

812

of the invention has a mean average diameter desirably less than about 300 nanometers, preferably between about 50 and 250 nanometers, typically about 200 nanometers. The mean average length of the carbon nanofibers is desirably between about 0.5 and 300 micron, typically about 200 micron. The graphitic carbon nanofibers can have a BET surface area between about 15 and 50 m

2

/g, typically between 15 and 30 m

2

/g. Such graphitic carbon nanofibers can be in the form of individual fiber strands including agglomerates of such fiber strands. A preferred graphitic carbon nanofiber for use in the cathode mixture

812

of the invention is a vapor grown graphitic carbon fiber available under the trade designation PR19HT carbon fibers from Applied Sciences, Cedarville, Ohio. Such graphitic carbon nanofibers can be made by hydrocarbon vapor pyrolysis methods described, for example, in Applied Sciences U.S. Pat. Nos. 6,156,256; 5,846,509; and 5,594,060 herein incorporated by reference. The resulting carbon nanofibers have a graphitic carbon structure as defined in International Committee for Characterization and Terminology of Carbon (ICCTC, 1982), published in the

Journal Carbon

, Vol. 20, p. 445. The vapor grown carbon fibers described in the above patent references are graphitic carbon fibers which can be made by the pyrolysis of hydrocarbon, for example, methane in a gas phase reaction at temperatures of around 1000° C. or higher. The gas phase reaction involving the hydrocarbon is carried out upon contact with metal particles, typically iron particles in a nonoxidizing gas stream. The iron particles catalyze the growth of very thin individual carbon fibers (e.g. carbon nanofibers) which have a graphitic carbon structure. The resulting carbon fibers can have a very thin diameter (nanofibers), for example, between 50 and 300 nanometers such as that available under the trade designation PR19HT graphitic carbon nanofibers (Applied Sciences).

It has been determined that the iron (or other metal) impurity which are residual catalyst impurities imbedded in the graphitic carbon nanofiber can be readily removed therefrom by subjecting the nanofibers to heating at temperatures between about 2500° C. and 3100° C. after the fibers have been formed. Such heating vaporizes the metal impurities and can also serve to further graphitize the carbon fiber, particularly the surface of the fibers. The end result is a purified graphitic carbon nanofiber desirably contains less than 200 ppm, preferably less than 100 ppm, more preferably less than 50 ppm metal. (The term metal shall include all metal whether in elemental, ionic or chemically bound in compounds.) Such graphitic carbon nanofiber can form a portion of the graphitic carbon material to be added to the AgCuO

2

cathode active material. For example, such graphitic carbon nanofiber can be admixed with natural graphite or expanded graphite as above mentioned.

The cathode mixture

812

comprising AgCuO2 includes an aqueous KOH electrolyte solution and the mixture can be prepared wet, with aqueous KOH included before the mixture is inserted into the cell. For example, the casing

820

can be filled with the cathode mixture and the central portion of the cathode mixture can be excavated leaving the annular cathode

812

as shown in FIG.

1

. The wet cathode mixture can be compacted while in the cell. Alternatively, the wet mixture can be compacted into disks

812

a

before insertion into the cell and then, optionally, additionally compacted while in the cell. Alternatively, the cathode mixture

812

can be prepared by first dry mixing the silver copper oxide, and graphite material optionally added. The dry mixture can be compacted into the cell casing

820

or can be compacted into disk shaped blocks

812

a

, which can be inserted into the cell in stacked arrangement. A separator sheet

890

can be placed against the inside surface of cathode disks

812

a

. Separator

890

can be of cellulosic film or a film formed of nonwoven material comprising polyvinylalcohol and rayon fibers. Separator

890

can be of a single layer of such nonwoven material or can be a composite having layer of cellophane adhered to the nonwoven material. The nonwoven material can typically contain polyvinylalcohol fibers and rayon fibers. Separator

890

can be positioned so that the cellophane layer is adjacent to either cathode

812

or anode

815

. Separators conventionally used in zinc/silver oxide alkaline cells can be used advantageously for separator

890

in the present cell

810

having a cathode

812

comprising silver copper oxide. Separator

890

can be prepared from a radiation graft of methacrylic acid onto a polyethylene membrane. Separator

890

in such form retards the migration of copper and silver ions to the anode compartment. AgCuO

2

has a slight solubility (e.g. less than about 1 weight percent) in aqueous potassium hydroxide. Thus, a small amount of the silver and copper ions from AgCuO

2

are present in solution within the aqueous potassium hydroxide electrolyte present in the cathode mixture

815

. The grafted separator is particularly desirable since it tends to retard migration of silver and copper ions from the cathode to the anode. Aqueous KOH electrolyte can be poured over the dry cathode wherein it becomes absorbed into the separator and cathode. The anode material

815

can then be added to the cell.

The silver copper oxide (AgCuO

2

) can be prepared by the reaction between a silver nitrate (AgNO

3

) and copper nitrate, (CuNO

3

) utilizing an oxidizing solution of KOH and K

2

S

2

O

8

with the reaction carried out at about 90° C. temperature. A method of synthesis according to the above reaction is described in J. Curda, W. Klein, and M. Jansen, “AgCuO

2

Synthesis, Crystal Structure, . . . ”,

Journal of Solid State Chemistry

, Vol. 162, pp. 220-224 (2001). Specifically, as stated in the above reference, microcrystalline AgCuO

2

can be synthesized by reacting saturated aqueous solution of 1.205 g (5 mMol) of AgNO

3

(Merck, 99%) and 0.85 g (5 mMol) of Cu(NO

3

)

2

H

2

O by adding a solution of 3.0 g of KOH and 1.5 g of K

2

S

2

O

8

in 150 ml of water at 90° C. The microcrystalline AgCuO

2

forms as a precipitate. The unique microcystalline structure of the AgCuO

2

is illustrated in

FIG. 6

of the above reference. The AgCuO

2

precipitate is filtered off, washed with deionized water and dried in air at 70° C. Another means of forming AgCuO

2

(alluded to in the above reference) is by oxidation of an aqueous suspension of Ag

2

Cu

2

O

3

as reported in the reference K. Adelsberger, J. Curda, S. Vensky, and M. Jansen,

J. Solid State Chem

., Vol. 158, p. 82 (2001). A method of preparing Ag

2

Cu

2

O

3

is given in K. Adelsberger et. al., supra,

J. Solid State Chem

., Vol. 158, at p. 82, as follows: “Black crystals of Ag

2

Cu

2

O

3

can be prepared by solid state reaction of Ag

2

O (precipitated from an acidic AgNO

3

solution) and CuO (Aldrich, 99%) in a high oxygen pressure. The binary oxides can be mixed in a 1:1 molar ratio and then annealed for 3-5 days in silver crucibles placed in stainless steel autoclaves. The optimized reaction temperature and oxygen pressure are 500° C. and 200 Mpa, respectively. One milliliter of a 7 M KOH aqueous solution is added as an accelerator. Microcrystalline, black powder of Ag

2

Cu

2

O

3

is precipitated from an aqueous solution of AgNO

3

(Merck, p.a., 99.5%) and CuNO

3

.3H

2

O (Panreac, p.a., 99.98%) adding 4 ml NaOH solution (3M). The precipitate is dried in air at 90° C. for 24 hours.”

The silver copper oxide prepared by the above methods can be used in cathode mixture

812

. The silver copper oxide for use in cathode

812

is a powder having an average particle size (dry) between about 1 and 100 micron. The silver copper oxide, AgCuO

2

, has a real density of about 7.1 g/cc and a BET surface area of about 10-100 m

2

/g, for particles sizes between about 1 and 100 micron. The Ag

2

Cu

2

O

3

has a real density of about 7.0 g/cc. The real density of a solid is the weight of the sample divided by the real volume. The real volume of a sample is the actual volume less volume occupied by entrapped air between the particles and pores within the particles. The BET surface area (m

2

/g) (Brunauer, Emmett and Taylor method) is the standard measurement of particulate surface area by gas (nitrogen and/or other gasses) porosimetry as is recognized in the art. The BET surface area measures the total surface area on the exterior surface of the particle and also that portion of surface area defined by the open pores within the particle available for gas adsorption and deadsorption when applied.

Anode

815

comprises zinc and aqueous KOH electrolyte. The electrolyte in the anode comprises a conventional mixture of KOH, ZnO and gelling agent. The zinc serves as the anode active material. The anode and cathode can be separated by a conventional ion porous separator

890

, for example, comprising polyvinylalcohol and cellulosic fibrous material. After cell

810

is filled an insulating plug

860

is inserted into open end

816

. Insulating plug

860

may be of polypropylene, talc filled polypropylene, sulfonated polyethylene or nylon. Plug

860

can have a thinned portion

865

therein typically of a small circular, oval or polygonal shape. Thinned portion

865

functions as a rupturable membrane which can be designed to rupture thereby releasing excessive gas within the cell. This guards against excessive buildup of gas pressure within the cell, for example, if the cell is subjected to excessive heat or abusive operating conditions. The plug

860

is preferably snap fitted around circumferential step

818

as shown in the figure so that the plug locks in place into the open end

816

. The peripheral edge

827

of casing

820

is crimped over the top of insulating plug

860

. A paper insulating washer

880

is applied over the crimped peripheral edge

827

of casing

820

. Insulating washer

880

can be a polyethylene coated paper washer. A terminal end cap

830

is welded to the head of current collector

840

. An elongated current collector

840

is then inserted (force fitted) into aperture

844

of insulating plug

860

so that end cap

830

comes to rest against insulating washer

880

. Current collector

840

can be selected from a variety of known electrically conductive metals found to be useful as current collector materials, for example, brass, tin plated brass, bronze, copper or indium plated brass. The current collector

840

used in the test cells was of brass. Conventional asphalt sealant may be preapplied around the current collector

840

before it is inserted into aperture

844

. A film label

870

is applied around casing

820

. The terminal end cap

830

becomes the negative terminal of alkaline cell

810

and pip

825

at the closed end of casing

820

becomes the positive terminal.

The cell

810

shown in

FIG. 1

can be an AA cell. However, the alkaline cell shown in the figure is not intended to be restricted to any particular size. Thus, the present invention is applicable to AAAA, AAA, C and D size cylindrical alkaline cells as well as button size or prismatic alkaline cells of any size or shape. Alkaline cell

810

is not intended to be restricted to any particular cell chemistry or cell size, except that the cathode

812

is prepared utilizing the cathode mixture of invention comprising silver copper oxide and graphite material. The above cell (

FIG. 1

) can be an AAAA, AAA, AA, C or D cells. These standard cell sizes are recognized in the art and are set by the American National standards Association or in Europe by the International Electrotechnical Commission (IEC). The AA cylindrical cell as referenced herein had standard overall dimensions as given by the American National Standards Institute (ANSI) battery specification ANSI C18.1M, Part 1-1999 as follows: The overall length from positive and negative terminal tips is between 49.2 mm and 50.5 mm and overall outside cell diameter is between 13.5 mm and 14.5 mm.

Thus cell

810

can contain conventional alkaline cell zinc anode chemistries including those which contain zero added mercury (less than 50 parts mercury per million parts total cell weight, preferably less than 10 parts mercury per million parts total cell weight) and modifications thereof. Such representative chemistries, for example, are disclosed in U.S. Pat. No. 5,401,590, herein incorporated by reference. The cell

810

of the invention also preferably does not contain added amounts of lead and thus can be essentially lead free, that is, the total lead content is less than 30 ppm, desirably less than 15 ppm of total metal content of the anode.

An alkaline cell having a gelled zinc anode and the cathode of the invention comprising silver copper oxide cathode active material (AgCuO

2

, Ag

2

Cu

2

O

3

or mixtures thereof) can also be fabricated in the form of a button or coin cell

110

as shown in FIG.

2

. The cell

110

can include a cathode

170

comprising the cathode mixture of the invention. Such cathode mixtures, can comprise silver copper oxide, 82 to 90 wt. %, graphite, for example, expanded graphite, between about 4 and 10 wt. %, and between about 5 and 10 wt. % of aqueous KOH electrolyte (aqueous KOH electrolyte is 30 to 40 wt. % KOH concentration, preferably between 35 and 40 wt. % KOH concentration). The aqueous KOH electrolyte preferably also contains about 2 wt. % ZnO. The cathode mixture can optionally also comprise between about 0.1 to 0.5 wt % of a polyethylene binder.

The anode material

150

comprises: Zinc alloy powder 62 to 69 wt % (99.9 wt % zinc containing indium), an aqueous KOH solution comprising 38 wt % KOH and about 2 wt % ZnO; a cross-linked acrylic acid polymer gelling agent available commercially under the tradename “CARBOPOL C940” from B. F. Goodrich (e.g., 0.5 to 2 wt %) and a hydrolyzed polyacrylonitrile grafted onto a starch backbone commercially available commercially under the tradename “Waterlock A-221” from Grain Processing Co. (between 0.01 and 0.5 wt. %); dionyl phenol phosphate ester surfactant available commercially under the tradename “RM-510” from Rhone-Poulenc (50 ppm). The zinc alloy average particle size is desirably between about 30 and 350 micron. The bulk density of the zinc in the anode (anode porosity) is between about 1.75 and 2.2 grams zinc per cubic centimeter of anode. The percent by volume of the aqueous electrolyte solution in the anode is between about 69.2 and 75.5 percent by volume of the anode. It shall be understood that the term zinc as used herein shall include such zinc alloy powder, since the alloy powder is composed almost entirely of zinc and functions electrochemically as zinc.

The separator

160

can be a conventional ion porous separator as described above with respect to separator

890

. In the specific embodiment shown in

FIG. 2

, referenced in the examples, the separator

160

comprises an outer layer of cellulose and an inner layer of a nonwoven material composed of cellulosic (rayon) and polyvinylalcohol fibers. The outer layer of cellulose abutted the cathode electrode.

In the button cell

110

shown in

FIG. 2

, a disk-shaped cylindrical housing

130

is formed having an open end

132

and a closed end

38

. Housing

130

is formed from nickel-plated steel. An electrical insulating member

140

, preferably a cylindrical member having a hollow core, is inserted into housing

130

so that the outside surface of insulating member

140

abuts and lines the inside surface of housing

130

. Alternatively, the inside surface of housing

130

can be coated with a polymeric material that solidifies into insulator

140

abutting the inside surface housing

130

. Insulator

140

can be formed from a variety of thermally stable insulating materials, for example, nylon or polypropylene.

The cathode mixture

170

comprising silver copper oxide (AgCuO

2

), graphite, aqueous electrolyte can be prepared by simple mixing at ambient temperature in a conventional blender until a homogenous mixture is obtained. The graphite can be flaky natural crystalline graphite, flaky crystalline synthetic graphite, expanded graphite or any mixture thereof. The cathode

170

is applied as a layer or a pressed disk abutting the inside surface of the closed end

138

of housing

130

. The separator sheet

160

is placed overlying cathode

170

. Additional aqueous electrolyte can be added so that electrolyte fully penetrates through separator sheet

160

and cathode

170

. A layer of anode mixture

150

comprising particulate zinc, aqueous KOH electrolyte solution (35-40 wt % KOH and 2 wt. % ZnO), and gelling agent is applied to the separator sheet

160

. The anode cover

120

, formed preferably of nickel-plated steel, is inserted into the open end

132

of housing

130

. An anode current collector

115

comprising a sheet of brass, tin-plated brass, bronze, copper or indium-plated brass can optionally be welded to the inside surface of anode cover

120

. Peripheral edge

135

of housing

130

is crimped over the exposed insulator edge

142

of insulating member

140

. The peripheral edge

135

bites into insulator edge

142

closing housing

130

and tightly sealing the cell contents therein. The anode cover

120

also functions as the negative terminal of the cell and the housing

130

at the closed end

138

functions as the cell's positive terminal.

Test cylindrical button cells

110

can be prepared, for example, having a diameter of 15.0 mm and depth of 6.98 mm.

In test button cells

110

the separator

160

can be a conventional ion porous separator consisting of an inner layer of a nonwoven material of cellulosic (rayon) and polyvinylalcohol fibers and an outer layer of cellophane. The same anode mixture comprising particulate zinc can be used in each test cell. The cathode composition can be varied. The performance of the cells, service life (milliamp-hrs) and energy output (milliwatt-hrs) can be determined by discharging at a given current, milliAmp or current density milliAmp/cm2 (current density at anode/cathode interface) to a specific cut off voltage, for example of 0.9 Volts.

In the tests reported in the following examples the test cells were AA cylindrical cells

810

of the type shown in FIG.

1

. In the case of the comparative test (Example 1) using an anode comprising zinc and a cathode comprising MnO

2

, the AA size cells

810

were balanced on the basis that milliamp-hrs capacity of zinc (based on 810 milliamp-hours per gram zinc) divided by the milliamp-hrs capacity of MnO

2

(based on 308 milliamp-hours per gram MnO

2

) is about 1. In the cells tested (Examples 2) using an anode comprising zinc and cathode comprising silver copper oxide (AgCuO

2

) or (Ag2Cu2O3). The AA size cells

810

were balanced on the basis that the milliamp-hrs capacity of zinc (based on 810 milliamp-hours per gram zinc) divided by the milliamp-hrs capacity of silver copper oxide and MnO

2

in the cathode mixture (based on 526 milliamp-hours per gram AgCuO

2

, 412 milliAmp-hrs per gram Ag

2

Cu

2

O

3

, and 308 milliamp-hrs per gram MnO

2

) is in slight excess of 1.

EXAMPLE 1

(Comparative—Zinc Anode; MnO2 Cathode)

Test cylindrical AA cells of the general configuration shown in

810

(

FIG. 1

) were prepared. Test cells

810

were prepared with a anode

815

comprising Zinc alloy powder 62 to 69 wt % (99.9 wt % zinc containing indium), an aqueous KOH solution comprising 38 wt % KOH and about 2 wt % ZnO; a cross-linked acrylic acid polymer gelling agent available commercially under the trade name “CARBOPOL C940” from B. F. Goodrich (e.g., 0.5 to 2 wt %) and a hydrolyzed polyacrylonitrile grafted onto a starch backbone commercially available commercially under the tradename “Waterlock A-221” from Grain Processing Co. (between 0.01 and 0.5 wt. %); dionyl phenol phosphate ester surfactant available commercially under the tradename “RM-510” from Rhone-Poulenc (50 ppm). The zinc alloy average particle size is desirably between about 30 and 350 micron. The bulk density of the zinc in the anode is between about 1.75 and 2.2 grams zinc per cubic centimeter of anode. The percent by volume of the aqueous electrolyte solution in the anode is between about 69.2 and 75.5 percent by volume of the anode. The separator

890

was a conventional dual layered cellulosic separator employing an outer layer comprising rayon and polyvinylalcohol (facing cathode

812

) and inner layer of cellophane facing anode

815

.

The cathode

812

has the following representative composition: 80-87 wt % of electrolytic manganese dioxide (e.g., Trona D from Kerr-McGee), 4-10 wt % of expanded graphite (Timcal E-BNB90, BET surface of 24.3 m

2

/g ), 5-10 wt % of an aqueous KOH solution having a KOH concentration of about 35-40 wt. %. The cathode

812

had 9.59 grams of MnO

2

and was balanced with an amount of zinc in anode

815

calculated as above described so that the theoretical capacity of the zinc divided by the theoretical capacity of the MnO

2

was about 1. A specific cathode composition which was used for Example 1 is as follows:

Cathode Composition

1

Wt. %

MnO

2

(EMD)

87

Expanded graphite

7

(Timcal E-BNB90)

KOH aqueous

6

Solution (36 wt %

KOH and 2 wt % ZnO)

100

Notes:

1. Conversion to volume percent can be made using the following real densities: MnO

2

(EMD), 4.48 g/cc; expanded graphite (Timcal E-BNB90), 2.25 g/cc; and 36 wt % KOH aqueous solution, 1.35 g/cc.

The AA cells

810

of Example 1 were discharged at a constant rate of 250 milliAmp (current density of about 21 milliAmp/cm

2

) to a cut off voltage of 0.9 volts. In separate tests batches of fresh AA cells

810

of Example 1 were discharged at a constant rate of 1 Amp.

At discharge of 250 milliAmp, the capacity obtained at a cut off voltage of 0.9 Volts was 2227 milliAmp-hrs. The specific capacity of the MnO

2

was 232 milliAmp-hours per gram. The energy output of the cell was 2004 milliwatt-hrs.

At discharge of 1 Amp, the capacity obtained at a cut off voltage of 0.9 Volts was 917 milliAmp-hrs. The specific capacity of the MnO

2

was 95.5 milliAmp-hours per gram. The energy output of the cell was 825 milliwatt-hrs.

EXAMPLE 2

Test AA size cells

810

were prepared as in Example 1 except that the cathode

812

is formed of the following cathode mixture of the invention comprising silver copper oxide (AgCuO

2

). The anode composition comprising gelled zinc was the same as used in Example 1. The cell has 10.3 grams AgCuO

2

and was balanced so that the theoretical capacity of the zinc divided by the theoretical capacity of the AgCuO

2

was about 1. The same composition of cathode was used except that the MnO

2

was replaced with AgCuO2. Graphite material in the form of expanded graphite was added.

Cathode Composition

1

Wt. %

AgCuO

2

87

Expanded graphite

7

(Timcal E-BNB90)

KOH aqueous

6

Solution (36 wt %

KOH and 2 wt. % ZnO)

100

Notes:

1. Conversion to volume percent values can be made using the following real densities: AgCuO

2

, 7.1 g/cc; expanded graphite (Timcal E-BNB90), 2.25 g/cc; and 36 wt % KOH aqueous solution, 1.35 g/cc.

The AA cells

810

of Example 2 were discharged at a constant rate of 250 milliAmp (current density of about 21 milliAmp/cm

2

) to a cut off voltage of 0.9 volts. In separate tests batches of fresh AA cell of Example 2 were discharged at a constant rate of 1 Amp.

At discharge of 250 milliAmp, the capacity obtained at a cut off voltage of 0.9 Volts was 2947 milliAmp-hrs. The specific capacity of the AgCuO

2

was 287 milliAmp-hours per gram. The energy output of the cell was 2652 milliwatt-hrs.

At discharge of 1 Amp, the capacity obtained at a cut off voltage of 0.9 Volts was 2210 milliAmp-hrs. The specific capacity of the AgCuO

2

was 207 milliAmp-hours per gram. The energy output of the cell was 1989 milliwatt-hrs.

EXAMPLE 3

Test AA size cells

810

were prepared as in Example 1 except that the cathode

812

is formed of the following cathode mixture of the invention comprising silver copper oxide (Ag

2

Cu

2

O

3

). The anode composition comprising gelled zinc was the same as used in Example 1. The cell had 9.86 grams of Ag

2

Cu

2

O

3

and was balanced so that the theoretical capacity of the zinc divided by the theoretical capacity of the AgCuO

2

was in slight excess of 1. The same composition of cathode was used except that the MnO2 was replaced with Ag

2

Cu

2

O

3

. Graphite material in the form of expanded graphite was added.

Cathode Composition

1

Wt. %

Ag

2

Cu

2

O

3

87

Expanded graphite

7

(Timcal E-BNB90)

KOH aqueous

6

Solution (36 wt %

KOH and 2 wt. % ZnO)

100

Notes:

1. Conversion to volume percent values can be made using the following real densities: Ag

2

Cu

2

O

3

, 7.0 g/cc; expanded graphite (Timcal E-BNB90), 2.25 g/cc; and 36 wt % KOH aqueous solution, 1.35 g/cc.

TABLE 1

AA Alkaline Cell With Zinc

Anode and Cathode Comprising AgCuO

2

Discharged at 250 milliAmp to 0.9 V

Specific

Capacity

Cathode

Active

Material

Capacity,

(MnO

2

or

mAmp-

Energy Out,

AgCuO

2

)

Example

Cathode

hrs

mWatt-hrs

mAmp-hrs/g

1 Com-

MnO

2

(EMD) and

2227

2004

232

parison

Expanded

Graphite

2

AgCuO

2

and

2947

2652

287

Expanded

Graphite

3

Ag

2

Cu

2

O

3

and

2247

2584

228

Expanded

Graphite

TABLE 2

AA Alkaline Cell With Zinc

Anode and Cathode Comprising AgCuO2

Discharged at 1 Amp to 0.9 V

Specific

Capacity

Cathode

Active

Material

Capacity,

(MnO

2

or

mAmp-

Energy Out,

AgCuO

2

)

Example

Cathode

hrs

mWatt-hrs

mAmp-hrs/g

1 Com-

MnO

2

(EMD) and

917

825

95.5

parison

Expanded

Graphite

2

AgCuO

2

and

2210

1989

207

Expanded

Graphite

3

Ag

2

Cu

2

O

3

and

1143

1315

116

Expanded

Graphite

As shown in Table 1 the alkaline cells of the invention with silver copper oxide cathode active material (Examples 2) discharged at 250 milliAmp exhibits a higher capacity and higher power output than the same size conventional Zn/MnO

2

alkaline cell discharged at same rate. The increase in capacity and power output of the alkaline cell of the invention with silver copper oxide cathode is more pronounced at higher discharge rate of 1 Amp as shown in Table 2.

Although the invention has been described with respect to specific embodiments, it will be appreciated that variations are possible within the concept of the invention. Thus, the invention is not intended to be limited to the specific embodiments herein described, but is better defined by the claims and equivalents thereof.

Alkaline cell with improved cathode

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